I've gone through the same process, since buying my Roubaix 2 years ago. It came with a positive stem and lots of spacers. I gradually lowered the stem, until all the spacers were above the stem, which I then reversed. I do experience some neck pain after about 2 hours, so I may have reached my flattest ride posture.

I haven't thought of the "bump" as being dangerous, until reading your post. Thanks!